CVE-2026-45271 picotls has infinite recursion in the minicrypto ASN.1 decoder

What is CVE-2026-45271?

CVE-2026-45271 is a medium-severity denial of service vulnerability in h2o picotls, published on 21 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

Official description

Picotls is a TLS protocol library that allows users select different crypto backends based on their use case. Picotls implements its own ASN.1 validation helper, which is used by the minicrypto backend while parsing local PKCS#8 private keys. Prior to commit c14231d801407640bc42c2dcf92783409ea6a7c7, the validator recursively descends into constructed ASN.1 elements without enforcing a maximum nesting depth. If an application loads an attacker-supplied private-key file through ptls_minicrypto_load_private_key(), or otherwise calls the public ASN.1 validation API on untrusted DER, a crafted deeply nested ASN.1 structure can exhaust the process stack and crash the application. Note that the libcrypto (OpenSSL) backend does not use the ASN.1 validation helper of picotls, and therefore is immune to this vulnerability. The vulnerability has been addressed in commit c14231d801407640bc42c2dcf92783409ea6a7c7.

Weakness: CWE-835

Which versions are affected by CVE-2026-45271?

How do I fix CVE-2026-45271?

No fix has been published for CVE-2026-45271 yet. Limit exposure of the affected software until one is available.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-45271 being exploited?

There is no known exploitation of CVE-2026-45271 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-84f5-m5x2-82q4.